Surgical lamps are typically attached to a room ceiling or wall, or a mobile stand by means of a so-called carrying system. Usually, the carrying system includes a first boom that is pivotable around a vertical axis, and a second boom that is horizontally pivotable and height-adjustable. It is possible to position the surgical lamp at a location in the room, where it is advantageous to illuminate the operation site.
An articulated suspension system allows the orientation of the surgical lamp and consequently the direction of the emitted light in the three rotatory degrees of freedom. In a simple version, the suspension system usually consists of a yoke approximately having the shape of a circular arc extending to a quadrant (quarter yoke), which is pivotable around a first vertical axis at its upper end, located at the outer end of the second boom of the carrying system. Also at the lower end of the yoke, a pivot joint is located, at which the lamp body of the surgical lamp is laterally attached, pivotably around a second horizontal axis (semi cardanic suspension). However, it is not possible to directly adjust certain light directions because the lamp body is merely pivotable around the horizontal axis. For adjusting certain light directions, the suspension system must first be pivoted around the vertical axis.
A second yoke (comfort yoke), which also includes a shape of a circular arc and extends to a quadrant, was introduced to remedy this disadvantage and to permit handling of the surgical lamp in a more comfortable way. The diameter of the second yoke is smaller than the diameter of the first yoke and both yokes are concentrically arranged around the virtual center of the first yoke.
At its first end, the second yoke is rotatably joined to the first yoke in the second pivot axis, and, at its second end, the lamp body is laterally attached pivotably around a third pivot axis. Therefore, the suspension system has three pivot axes. The first and the second axis are perpendicular to one another, and the second and the third axis are perpendicular to one another. Hence, it is possible to orientate the lamp body in any desired direction with a pivot movement around the second and/or third axis. Thus, it is possible to determine the direction of the light emission, as requested (full cardanic suspension).
However, this arrangement requires a considerable expenditure because of the additional yoke. In addition, the body and yokes occupy more installation space, and, due to increased weight, the operating force is increased. Furthermore, the height of the suspension system increases about 5 cm to 8 cm because of the additional space requirement for spinning of the quarter yoke below the vertical pivot joint. Thus, the head room below the lamp head is reduced.
Furthermore, the quarter yoke is exposed to high strain because of torque and torsion, respectively. Therefore, it is difficult to cause the two axes, which are offset by 90°, to traverse in the center of gravity of the lamp head (vertical offset). The angle deviation of the axes from the 90° angle, which is generated by the quarter circular shape of the quarter yoke, is a further problem because both pivot axes do not pass through the center of gravity of the lamp body (horizontal offset). Hence, it is necessary to keep pre-adjusted positions of the lamp head by strongly adjusted breaks which increase the operation force.
In some systems, a yoke having the shape of a half circular arc is pivotably arranged around its longitudinal axis, the yoke encompasses the lamp body, and the lamp body is pivotably mounted at both ends of the yoke. In this case, the second pivot axis is arranged in the space in an inclined manner, which increases the difficulty level of operation, and the lamp body cannot be pivoted around its center axis, which leads to problems in operation of the surgical lamp, particularly if the operating elements are arranged at the circumference of the lamp head. This way of operation is similar to the operation of a semi cardanic suspension.